A striker-type fire control mechanism is commonly used in modern semi-automatic pistols. In striker fired pistols, the trigger is connected to a trigger bar. Movement of the trigger causes movement of the trigger bar, which in turn causes a sear to rotate about a pivot point. Upon rotation of the sear, a spring is compressed and an upper portion of the sear is displaced relative to the firing pin. Upon displacing the sear a sufficient distance to clear a depending leg of the firing pin, the firing pin is urged forward by a spring and strikes the rear of the cartridge, thereby discharging the firearm. After the firearm discharges, the trigger must be released forward to a point where the trigger bar re-engages the sear, resetting the trigger for the next shot.
In some firearms, the trigger reset is aided by a single tensioning coil spring located forward of the magazine channel. This trigger return spring performs the dual role of returning the trigger to a forward position and pulling the rear end of the trigger-bar back under the sear. During the forward return of the trigger bar, but before re-engagement with the sear, the trigger bar is laterally displaced out of cooperation with the sear such that the firearm may not yet be fired. As the trigger bar continues to move forward, the rear end of the trigger bar is pulled back under the sear, re-engaging the sear so that the firearm is again ready to fire.
The mechanical impact that occurs between the trigger bar and sear upon re-engagement physically communicates to the operator, through the operator's finger on the trigger, that the trigger reset is complete and that the firearm may be fired, i.e., that the firearm is set to fire when the trigger is pulled back again. However, because this mechanical impact can be slight, the physical communication to the operator through the trigger is subtle, and thus it can be difficult for a firearm operator to ascertain when trigger reset has occurred.